[RE-wrenches] Hawaiian Tie in

Tue Aug 8 13:13:50 PDT 2023

The Feeder Tap is our preferred method when available. However, I think you
will find engineers who disagree that the tap can occur anywhere along the
feeder. In my experience, PEs want to see that tap done with the downstream
OCPD close to the tap. We would normally tap immediately before the
subpanel OCPD within the subpanel.

We use a "sum of breakers" and "120%" rule in combination for many
situations with meter/main panels and downstream subpanels. I've heard this
called the Hawaiian Mai-Tai and/or Mai-Tai with a twist depending on the
scenario.

The only issue I see potentially with Dana's Hawaii Tie-In example is
mixing feeder conductors and service conductors in the same raceway
(230.7). It's not completely clear what the intention is. I have seen some
inspectors take this to another level and try to apply 230.7 to enclosures,
but usually you can talk them through that unless they dig their heels in
and consider an enclosure or cabinet a raceway. You might also need to deal
with limitations in 312.8 regarding your splices.

Regarding the utility asking how you can have a 225 amp panel behind a 100
amp breaker, what business is that of theirs, and why the heck not?! In
Florida, once you leave the meter can, that's customer-owned equipment and
outside the utility's domain. There are millions of 200A residential
services with 225A load centers (bus rating). Maybe they are wondering how
you can do it because it is MLO, but that does not matter because the bus
is protected by the premises main OCPD.

One other consideration is whether you can even do this. If the combined
continuous inverter output current exceeds 80A, the conductors between the
main disconnect and the subpanel would need to be larger than #3 because
the subpanel is MLO and the backfed conductors need to be sized for 125% of
the inverter output current (regardless of the 100A OCPD in the meter
bank). And then the main disconnect itself would need to be greater than
100A, which would exceed the service rating. It's unclear what the actual
inverter output ratings are in the example drawing. Around here, we are
limited to 90% of the service rating by the utility, but that's a moot
point because you can't exceed 80% of the service rating due to the main
breaker needing to be 125% of the inverter output rating. I'm
oversimplifying this because the utility's 90% rule is not directly related
to the inverter output rating, but is 85% of the system DC rating (which is
pretty dumb).

Fun, fun, fun... Fortunately, we don't run into too many 100A services
around here.

Jason Szumlanski
Principal Solar Designer | Florida Solar Design Group
NABCEP Certified Solar Professional (PVIP)
Florida State Certified Solar Contractor CVC56956

On Tue, Aug 8, 2023 at 3:04 PM Dana Orzel via RE-wrenches <
re-wrenches at lists.re-wrenches.org> wrote:

> Correct  & The 225 amp bus bar gives us the busbar ampacity to accept the
> 120 amp back feed (includes the 25% factor)
>
> 22800w /240v = 95 amp
>
>
> On 8/8/2023 12:19 PM, Darryl Thayer via RE-wrenches wrote:
>
> I need clarification; however, here is my interpretation for you.
> The utility feeds the meter and then the 100A breaker.
> Then you want this 100A breaker to feed the 220A bus panel.
> This 220A panel then supplies through a 100A breaker the house load.
> The solar also feeds the 220A panel.  If the solar exceeds 100A, and the
> house load is small, the meter breaker will disconnect, losing power to the
> solar and the load.
>
> On Tue, Aug 8, 2023 at 10:11 AM Dana Orzel via RE-wrenches <
> re-wrenches at lists.re-wrenches.org> wrote:
>
>> Oh Wise folks!
>>
>> Attached is a wire schematic please review. & feel free to possibly use
>> for yourself in the future.
>>
>> I am in a bind with an interconnection where I have an apartment 6 pack
>> meter  box with all 120-240v/100 amp breakers & assumed 100 amp busbars.
>> The apts. were a mid 1970's original build.  There are 4 apartment with 1
>> circuit/meter each & 1 house circuit/ meter for owners use.The breaker
>> boxes are Sylvania (yuck). Originally I assumed a larger busbar due to 6 -
>> 100 amp breakers & this was not the case. We all know about assuming...
>>
>> I consulted with W-2 who had assisted my lead installer in in the past
>> from UT. He sent the following & though it makes sense to me, the utility
>> is asking how I can have a 225 amp panel behind a 100 amp breaker. My
>> response was that all we are doing is  achieving a properly sized bus bar
>> to accommodate the back feed.
>>
>> My Utility Idaho Power requires  interconnection with a meter that has a
>> load on it. Solar only meters are not allowed. This is for the owners loads
>> only & he has 1 meter per apt complex at 100amps each.
>>
>> I am wondering if any of you have used this connection adaption to
>> achieve a larger array connection & how it went?
>> --
>> Dana Orzel Great Solar Works, Inc. C - 208.721.7003 dana at solarwork.com
>> Idaho Contractor - # 028765 Idaho PV # 028374 "Responsible Technologies for
>> Responsible People since 1988"
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> --
> Dana Orzel Great Solar Works, Inc. C - 208.721.7003 dana at solarwork.com
> Idaho Contractor - # 028765 Idaho PV # 028374 "Responsible Technologies for
> Responsible People since 1988"
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